The silicone adhesives heretofore used to bond semiconductor chips to chip attachment sites have ranged from liquid curable silicone compositions to paste-like curable silicone compositions. These silicone adhesives have taken the form of curable silicone compositions comprising at a minimum an organopolysiloxane having at least 2 silicon-bonded alkenyl groups in each molecule, an organopolysiloxane having at least 2 silicon-bonded hydrogen atoms in each molecule, and a hydrosilylation reaction catalyst. Curable silicone compositions have also been used that additionally contain an adhesion promoter in the form of an organopolysiloxane containing in each molecule at least 1 silicon-bonded alkoxy group and at least 1 silicon-bonded alkenyl group or at least 1 silicon-bonded hydrogen atom (Japanese Patent Application Laid Open (Kokai or Unexamined) Number Hei 3-157474 (157,474/1991)).
However, low-viscosity silicone oil outmigrates from these curable silicone compositions during the time interval leading up to their complete cure, which has caused contamination of the environment surrounding the composition. This low-viscosity silicone oil--because it consists of low degree of polymerization (DP) organopolysiloxane present in the organopolysiloxane base component and/or low DP organopolysiloxane present in the organopolysiloxane added as adhesion promoter--has proven extremely difficult to completely eliminate. As a result, the use of these curable silicone compositions to bond a semiconductor chip to the chip attachment site has resulted in such problems as a reduced wire bondability (joinability) between the bonding pads on the chip and bonding wires or beam leads and a degradation in the reliability of the resulting semiconductor device.